Geochemical processes have created energy dense non-renewable organic feedstocks by concentrating and dehydrating biological materials. The chemical industry has since developed elegant and efficient methods for exploiting this valuable, yet limited, resource. In the event that current processes become uneconomical, supplementing petrochemical production by converting renewable bio-based feedstocks to marketable products will grow in importance. However, removing up to 50 weight percent water from biological materials while maximizing product selectivity poses significant challenges to the research community. Piperylenes, for example, are by-products of the petroleum industry and are important raw materials for the manufacture of plastics, adhesives and resins. Due to process improvements that reduce by-product formation, commercial piperylenes supplies are increasingly becoming limited. Decoupling of piperylenes from the petroleum industry may therefore provide an advantaged route to this valuable product.
The major component of this C5 mixture is 1,3-pentadiene and is commonly referred to as piperylene; 1,4-pentadiene is a minor component and can be isomerized to the 1,3-isomer. Catalytic dehydration of 2-methyl-tetrahydrofuran (2-Me-THF), a bio-derived feedstock, may provide a competitive alternative route to 1,3-pentadiene. Coverage of this reaction by the prior art is limited and lacking specific examples; however, it is clear that an acidic catalyst is necessary to carry out this transformation. Various metal oxides, phosphate salts and titanium dioxide supported on alumina reportedly perform the dehydration reaction. For example, a boron phosphate catalyst has been reported to convert 40% of 2-Me-THF to 1,3-pentadiene with 91% selectivity to give a single pass yield of 36% and a space-time-yield (STY) of 3.1 moles 1,3-pentadiene/Kg catalyst/h.
Secondary reactions such as piperylene polymerization and generation of gaseous decomposition products lead to yield loss in this reaction. Catalyst coking can also hinder performance as well as catalyst sensitivity to reactants and products, which can lead to catalyst deactivation. A preferred catalyst for this reaction would therefore demonstrate high 2-Me-THF conversion and high selectivity to pentadiene and maintain activity between runs.
Dehydration of other substrates such as mono-alcohols can afford useful alkene products while di-alcohol and cyclic ether substrates can lead to the corresponding dienes. For example, n-pentanol is expected to form a mixture of linear pentenes while pentane diols would form a mixture of pentadiene isomers. Tetrahydropyran and 3-methyl-tetrahydrofuran, both cyclic ethers, are expected to form pentadiene isomers and isoprene, respectively.
It is known that tri-alcohol substrates such as glycerol, a bio-diesel co-product, can be converted into acrolein upon dehydration. This product is the immediate commercial precursor to acrylic acid but is very reactive and prone to polymerization, particularly on acidic catalyst surfaces. Formation of hydroxyacetone (acetol) and acetone are also possible products from this reaction. Thus, catalytic dehydration of glycerol to acrolein can pose significant selectivity challenges.
A catalyst capable of facilitating the aforementioned dehydration reactions, and that is reusable and does not deactivate in the presence of copious amounts of water would be very useful.